Liquid nitrogen refrigeration system

ABSTRACT

The invention relates to a refrigeration system for a cargo container and a method of refrigerating the container in which the interior of the container is connected with a reservoir of liquid nitrogen, a control valve is provided between the container and reservoir to control admittance of nitrogen to the container and the control valve is caused to be opened and closed for predetermined time intervals. The control valve is opened and closed automatically by a timing device, which is preferably powered by pressure from within the reservoir of nitrogen. However, the timing device may be of any, known type.

United States Patent Hales et al.

[ Oct. 24,1972

[541 LIQUID NITROGEN REFRIGERATION SYSTEM 5 [73] Assignee: ShipownersRefrigerated Cargo Research Association, Cambridge,

England 22 Filed: Oct. 26, 1970 21 Appl. No.: 83,723

[30] Foreign Application Priority Data 3,092,974 6/1963 Haumann ..62/2313,258,931 7/1966 Kelly 1.62/514 3,287,925 11/1966 Kane ..62/5143,305,000 2/1967 Bullen ..62/514 3,552,143 1/1971 Johnson ..62/514Primary Examiner-Meyer Perlin Attorney-Baldwin, Wight & Brown [5 7ABSTRACT The invention relates to a refrigeration system for a cargocontainer and a method of refrigerating the container in which theinterior of the container is connected with a reservoir of liquidnitrogen, a control valve is provided between the container andreservoir to control admittance of nitrogen to the container and thecontrol valve is caused to be opened and closed for predetermined timeintervals. The control valve is opened and closed automatically by atiming device, which is preferably powered by pressure from within thereservoir of nitrogen. However, the timing device may be of any, knowntype.

3 Claims, 4 Drawing Figures PATENTEDncI 24 I972 SHEET 1 OF 3 SMNNMXMNQWREQU WSQ RM 4 X I I If I I I PATENTED our 24 I972 SHEET 2 [IF 3 m mIPATENTEUUBT 24 \972 sum 3 BF 3 HOP/START S 1 LIQUID NITROGENREFRIGERATION SYSTEM This invention relates to the refrigeration oftransportable containers. It is especially concerned with therefrigeration of containers which are used for the intercontinentaltransport of commodities where a low temperature and/or low humiditymust be maintained inside a container irrespective of wide variations inthe external temperature and humidity and notwithstanding handling bydifferent forms of transport.

According to the present invention a refrigeration system for acontainer of the kind specified comprises a reservoir containing liquidnitrogen, pipe means adapted to connect said reservoir to'the container,valve means in said pipe means arranged to admit pulses of liquidnitrogen into the container and control means adapted to open and closesaid valve for predetermined time intervals.

Preferably said valve means and control means are physically attached tothe liquid nitrogen reservoir for compactness.

Also according to the invention, we provide a method of refrigerating acargo container of the kind specified comprising connecting the interiorof the container with a reservoir of liquid nitrogen, providing acontrolvalve between the container and reservoir to control admittance ofnitrogen to the container and causing the control valve to be opened andclosed for predetermined time intervals.

In its simplest form, the control means merely comprises a timing deviceto open and close the control valve at preset time intervals.Alternatively, the control valve may be pressure operated, in whichcase, a further fiuidline extends from the top of the liquid nitrogenreservoir to the-control valve and the pressure operated control valveis powered by pressurized gas from the space above the liquidnitrogen insaid reservoir. In this arrangement a further valve may be provided inthe further fluid line, controlled by a timing device. This furthervalve may be a solenoid operated valve. The timing device may beelectrically or elec tronically operated, pressure operated, e.g. acontrolled build up of pressure to a predetermined maximum giving asignal at intervals, or clockwork or battery operated, or fluidiccontrol systems such as those described in our copending US. Pat.application Ser. No. 83,722 filed Oct. 26, 1970 now US. Pat. No.3,673,810 could be used. v

Several embodiments of the invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 shows schematically a container fitted with a refrigerationsystem according to the present invention, and

FIG. 2 shows schematically an electrical valve control arrangement foruse in the system of FIG. 1, and

Y According to one embodiment of the invention shown schematically inFIG. 2, supply of nitrogen to the spray header H is controlledelectrically. The control system Z of FIG. 2 includes a solenoidoperated valve S in the pressure fluid line between the nitrogen vaporin the top .of the tank T and the pressure operated control valve X. Thevalve S is simply turned on and off for equal predetermined timeintervals by an electric or electronic timer E obtaining its power froma power supply P, thereby opening and closing the valve X forpredetermined intervals of time.

In a simplified version of the embodiment of FIG. 2, the control systemZ merely comprises a timing device which maybe electrically or clockworkoperated or operated by other means directly to open and close forpredetermined periods of time the control valve X. It will beappreciated that in the embodiment of FIG. 2, the timer E may beoperated mechanically, on a time clock principle of operated in othermanner. It will be appreciated, however, that in the preferredarrangements, the vapor pressure of the nitrogen in the cylinder T isused to power the control system. Alternative control systems are shownin FIGS. 3 and 4 and described more fully in our co-pending applicationSer. No. 83,722, now US. Pat. No. 3,673,810. Generally speaking,however,.the alternative control systems are of the fluidic type. Onpressing a start button, a fluidic delay device is set in motion and asignal pressure is applied to the valve X which opens the valve andcauses liquid nitrogen to flow into the container. After a suitablepredetermined interval of time, the valve is closed and liquid nitrogenceases to flow. There is then a further time delay before the sequenceis repeated. On pressing a stop button, the time sequence is interruptedand no further output signals are made to the valve X. In the event offailure of the control system, a 'zero output pressure to valve X closesthe valve.

The control system is such that the timing sequence can be variedaccording to the ambient temperature surrounding the container. Thisambient temperature can be used, by making use of thermostats,automatically to vary the time delay of the fluidic delay units therebycontrolling the time during which the valve X is opened. Such automaticcontrol can also be used with the FIG. 2 embodiment.

In the embodiment shown in FIG. 3, a NOR logic unit N employing twoinputs and two outputs is connected to a restrictor R and a volume V andin series with an equal number of similar NOR units complete withrestrictors and volumes to form a closed loop L. An output 0 from theNOR UNIT N is connected to and controls the valve X. The system producesequal on and off timing intervals and the total cycle time can beincreased or decreased by the use of multiport valve M for switchinginto and out of the closed loop further pairs of NOR units complete withrestrictors and volumes in series thereby shortening or lengthing thecircuit and hence the time delay produced by the circuits. The multiportvalve M can be set either manually or automatically according to theambient temperature surrounding the container C.

In the embodiment of FIG. 4, the cycle of operations is initiated by aconventional stop start system S which uses two NOR logic units NORl,NOR2, cross connected to provide a simple flip-flop. A closed loop L,

3 L", respectively comprising an equal number of NOR units, volumes andrestrictors arranged in series is connected to the output of each NORunit and upon applying a start signal to the NOR unit NOR 2, an outputfrom the other NOR unit NORl opens the valve X and the series NOR unitsin the closed loop L" with their respective volumes and restrictorscontrol the duration of. the valve opening. When this output is fed backto the other NOR unit NORl as an input signal, an output signal from theNOR unit NOR2 goes through the respective delay NOR units with theirrestrictors and volumes in the loop L until it is fed back as an input,thereby automatically restarting the cycle. The time delay can be variedby switching in, by means of a multiport valve M, further pairs of NORunits into one or both of the closed loops L, I." as in the embodimentof FIG. 3, or by varying the volume in series with any NOR unit.

What is claimed is:

1. A refrigeration system for a'containe r comprising a reservoircontaining liquid nitrogen and nitrogen vapor, first pipe means forconducting liquid nitrogen from said reservoir to said container, acontrol valve in said first pipe means arranged to admit pulses ofliquid nitrogen into the container, control means for opening andclosing said control valve for predetermined time intervals, saidcontrol means includes a portion thereof disposed in second pipe meansfor conducting nitrogen vapor from said reservoir to said control valve,said control valve being responsive only to pressure of said nitrogenvapor in said reservoir to admit pulses of liquid nitrogen into thecontainer through said first pipe means, said control means portion is avalve in said second pipe means controlled by a timing device, and

said timing device is electrically operated.

2. A refrigeration system for a container comprising a reservoircontaining liquid nitrogen and nitrogen vapor, first pipe means forconducting liquid nitrogen from said reservoir to said container, acontrol valve in said first pipe means arranged to admit pulses ofliquid nitrogen into the container, control means for opening andclosing said control valve for predetermined time intervals, saidcontrol means includes a portion thereof disposed in second pipe meansfor conducting nitrogen vapor from 'said reservoir to said controlvalve, said control valve being responsive only to pressure of saidnitrogen vapor in said reservoir to admit pulses of liquid nitrogen intothe container through said first pipe means, said control means portionis a valve in said second pipe means controlled by a timing device, andsaid timing device is electronically operated.

3. A refrigeration system for a container comprising a reservoircontaining liquid nitrogen and nitrogen vapor, first pipe means forconducting liquid nitrogen from said reservoir to said container, acontrol valve in said first pipe means arranged to admit pulses ofliquid nitrogen into the container, control means for opening andclosing said control valve for predetermined time intervals, saidcontrol means includes a portion thereof disposed in second pipe meansfor conducting nitrogen vapor from said reservoir to said control valve,said control valve being responsive only to pressure of said nitrogenvapor in said reservoir to admit pulses of liquid nitrogen into thecontainer through said first pipe said timing device is clockworkoperated.

1. A refrigeration system for a container comprising a reservoircontaining liquid nitrogen and nitrogen vapor, first pipe means forconducting liquid nitrogen from said reservoir to said container, acontrol valve in said first pipe means arranged to admit pulses ofliquid nitrogen into the container, control means for opening andclosing said control valve for predetermined time intervals, saidcontrol means includes a portion thereof disposed in second pipe meansfor conducting nitrogen vapor from said reservoir to said control valve,said control valve being responsive only to pressure of said nitrogenvapor in said reservoir to admit pulses of liquid nitrogen into thecontainer through said first pipe means, said control means portion is avalve in said second pipe means controlled by a timing device, and saidtiming device is electrically operated.
 2. A refrigeration system for acontainer comprising a reservoir containing liquid nitrogen and nitrogenvapor, first pipe means for conducting liquid nitrogen from saidreservoir to said container, a control valve in said first pipe meansarranged to admit pulses of liquid nitrogen into the container, controlmeans for opening and closing said control valve for predetermined timeintervals, said control means includes a portion thereof disposed insecond pipe means for conducting nitrogen vapor from said reservoir tosaid control valve, said control valve being responsive only to pressureof said nitrogen vapor in said reservoir to admit pulses of liquidnitrogen into the container through said first pipe means, said controlmeans portion is a valve in said second pipe means controlled by atiming device, and said timing device is electronically operated.
 3. Arefrigeration system for a container comprising a reservoir containingliquid nitrogen and nitrogen vapor, first pipe means for conductingliquid nitrogen from said reservoir to said container, a control valvein said first pipe means arranged to admit pulses of liquid nitrogeninto the container, control means for opening and closing said controlvalve for predetermined time intervals, said control means includes aportion thereof disposed in second pipe means for conducting nitrogenvapor from said reservoir to said control valve, said control valvebeing responsive only to pressure of said nitrogen vapor in saidreservoir to admit pulses of liquid nitrogen into the container throughsaid first pipe means, said control means portion is a valve in saidsecond pipe means controlled by a timing device, and said timing deviceis clockwork operated.